Data from any spacecraft would be acceptable but the spacecraft would have to
be in the right region of geospace. The definition of the magnetotail would
necessarily be approximate because the size and shape of the magnetosphere are
significantly altered by the magnetic storms themselves. The definition of a
geomagnetic storm would involve reference to a secondary data source e.g. a
storm might be counted as an interval when the Dst index dip below -100nT.

Retrieve the Dst index for the period of interest from any one of a number of sites holding it.

Process the Dst dataset using custom code to identify those times when the index dipped below -100nT.

Identify a list of suitable candidate spacecraft using personal knowledge of which spacecraft have orbits which take them inside the magnetosphere and have a magnetometer on board.

BEGIN Iteration over spacecraft

1 Locate an on-line source of data for that spacecraft and request data for a time window around each magnetic storm. This would probably require multiple requests and registration and authentication might also be necessary, even for data with no access restrictions.

Process the retrieved spacecraft data to select those observations when the spacecraft was in the magnetotail.

Convert the position data to a defined coordinate system and the magnetic field data to specific units. The appropriate coordinate system will depend on the application, but in this example it would be Geocentric Solar Magnetospheric (GSM), and the magnetic field would be expressed in nanoTeslas (nT).

It is reasonable to hope that the Grid would automate all six enumerated
steps. Issues raised :

"nesting" queries

the definition of the periods of interest is in terms of the value of an index, which would itself have to be located and extracted from a remote database.

selecting among multiple data sources providing the same data.

the ability to process data (albeit simple data) in the course of a query.

the dataset metadata must identify the regions where spacecraft flew.

again, the need to process the position data in order to select data of interest. Ultimately, it might be nice for the system to be able to use magnetic field models nehind the scenes, but that is not the first priority.

automatic conversion of position data to and from various coordinate systems is necessary, plus automatic conversion of data values.

What is described is simply data acquisition. How the data should be
presented would be highly dependent on the analysis to be done, for example an
event-based study or a statistical survey. A generic display tool for
generating time series stackplots would be useful for an event-based study,
but frequently the most useful output of the system would be simply a
collection of time-ordered datasets, or a single composite dataset, with the
data from multiple sources presented in a common set of coordinates and units.
Generic routines for Matlab, IDL etc. for extracting data from the standard
(XML-based?) data format would be useful.

GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Science Problems Forum. For other ScienceProblems, refer to the ScienceProblemList.Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.